It is known in the art relating to automotive engine manufacture and timing the camshafts of engines to loosely install the sprockets on the camshafts to allow free rotation of the sprockets, lock the camshafts into an index position, install the timing belt on the drive sprockets, rotate the engine several times to seat the belts (with the sprockets free-wheeling on the camshafts), index the crankshaft to a predetermined position, and then lock the sprockets onto the camshafts.
Previous arrangements for mounting the sprockets on the camshafts required that the nose of the camshaft be hardened and have a special profile with very precise size tolerances, the sprocket have a counterbore spaced from the shaft, two rings fitting into the space between the shaft and counterbore, a washer for pushing the rings into the space with a specific force to achieve a press fit, and a bolt threaded into the shaft end to push the washer against the rings. During the free-wheeling part of the timing operation the bolt is not yet tightened and the sprocket tips excessively due to limited support or alignment control. During tightening, the press force must be monitored.
It has also been proposed to use tapered rings and shafts for the coupling with sprockets but they tend to bind the sprocket or lock up during free wheeling, and they pop out of position under load and can not prevent the sprocket from tipping.